Extracellular antibiotics produced by ectomycorrhizal fungi have been suggested as one form of root protection against infection by phytopathogenic fungi (Zak, Ann. Rev. of Phytopath., 2, pgs. 377-392, 1964).
The production of antibiotic `in vitro` by mycorrhizal has been reported in over 100 fungi (Marx, Ectomyco., pgs. 351-382, 1973). One such microorganism, Pisolithus tinctorius, has been shown to improve the growth of infected plants as described in U.S. Pat. No. 4,550,527.
A number of researchers have tried to isolate an active compound from the liquid culture of the fungus. Pisolithus tinctorius. Naphthalenoid pulvinic acid derivatives, a trieterpenoid (pizolactone), humic acid like compounds and others have been isolated from this fungus, but none of them exhibit and suggest an antifungal activity (K. H. Tan et al., Soil Sci. Soc. Am. J., vol. 42, p. 906-908, 1978; M. Gill et al., Phytochemistry, vol. 24, no. 6, pp. 1351-1354, 1985; A. M. Lobo et al., Tetrahedron, vol. 24, no. 21, pp. 2205-2208, 1983). A compound possessing antifungal activity has never been isolated.
Accordingly, since the antifungal activity of Pisolithus tinctorius has never been ovserved, there existed no reason for attempting to isolate the biofungicidal factor or factors which are generated in a liquid culture of this fungus.
However, if Pisolithus tinctorius produces antibiotic metabolites, it would be highly desirable to find a way of isolating them and using them to destroy undesirable fungi which grow not only on plants but also, for example, on the skin of animals thereby causing dermatomycosis.